There are more than one detailed posts about this. But I rather answer than look for it.

I have 5box fished with 90% catching. So rather efficient. I used innerspace + mousebroadcasting. Just make sure your clients all have the same aspect ratio so the mousebroadcasting is precise. Start a straight walk to the water with toons on follow. Move each toon on top of the first toon (Bonus points if you dont have different height characters). Calibrate the camera by using default cam settings (page up/ page down I believe). After that finetune the rotation by quick swapping the alt views on the main view. Start with first toon, find a recognizable point, put your mouse cursor on it, swap screen, drag mouse to that point. Quick Swap a few times to check if is matching. Start again with toon one, find that point, swap to toon three. Etc. Once all views are the same, start fishing (use macro like /cast [nochanneling] fishing). Maybe a macro for lures and such).

Hmm steps are more readable:
1. get innerspace
2. make sure all ratio's are the same accross toons
3. move all toons on same spot
4. calibrate toon 2 3 .... on toon 1 view with exact same camera settings on one solid spot (practice makes perfect)
5. mousebroadcast on and start fishing with no channeling macro so you can keep spamming (make sure you dont accidentally change view due to unstable clicks ( I prefer to use a trackball for this kind of stuff ).

Learn to find the finesse of bobbers almost on top of each other. Even when they are on top of each other you should be able to unique click them. The better the views match, the higher the quality. Try to zoom in so you have the full screen for bobbers, and dont just use a small portion. The bigger the screen estate the finer the mousebroadcast.